Plunger tack

ABSTRACT

There is provided a plunger tack for transmitting driving force to a deformable plunger adapted to be disposed in a compressed configuration in sliding, sealing engagement within a medicament containing chamber of a hypodermic device. The tack includes a rearwardly exposed flange for engagement with a driving member such as a movable piston, and an axially extending shank received within a recess in the plunger and retained therein solely by frictional forces when the plunger is in the compressed configuration. The shank is arranged to transmit the driving forces to a forward portion of the plunger to provide the plunger with an elongated, deformed configuration of reduced lateral dimensions and to thereby reduce the static frictional force developed between the plunger and sidewall of the chamber.

United States Patent 191 1111 3,809,082 May 7,1974

Hurschman PLUNGER TACK- [75] Inventor: Alfred A. Hurschman, Hudson,

' Ghio [73] Assignee: Ampoules, lnc., Macedonia, Ohio [22] Filed: Dec. 30, 1971 [21] Appl. No.: 213,902

521 U.S. Cl. 128/218 P [51] Int. Cl A6lm 5/22 [58] Field of Search.... 128/215, 216, 218 R, 218 P,

128/218 PA, 218 D, 218 F, 219, 272

[56] References Cited UNITED STATES PATENTS 1,139,368 -s/1915 Pierce.,....'.... 128/218 P 3,147,753 9/1964 Nogier et al..... 128/218 P 1,540,126 6/1925 Hein 128/219 2,660,168 11/1953 Pontius 128/218 P 3,543,755 12/1970 Kessel 128/218 P 2,267,074 12/1941 Brockway 128/272 2,895,773 7 1959 McConnaughey 128/218 P Primary ExamineF-Richard A. Gaudet Assistant Examiner-J. C. McGowan Attorney, Agent, or Firm-McNenny, Farrington, Pearne & Gordon [5 7] ABSTRACT There is provided a plunger tack for transmitting driving force to a deformable plunger adapted to be disposed in a compressed configuration in sliding, sealing engagement within a medicament containing chamber of a hypodermic device. The tack includes a rearwardly exposed flange for engagement with a driving member such as a movable piston, and an axially extending shank received within a recess in the plunger 9 Claims, 3 Drawing Figures 'PATENTEDIAY 1 i914 sii BACKGROUND OF INVENTION This invention relates to hypodermic devices that provide a cylindrical chamber containing a medicament to be injected and a plunger arranged for driven, forward movement within the chamber to advance the medicament and perform the injection function and, more particularly, to a plunger tack positioned adjacent a rearward portion of the plunger for transmitting driving force to the plunger to facilitate movement thereof.

The hypodermic devices with which the plunger tack of the present invention are useful include both needle and needleless type devices which may be used for subcutaneous or intra-muscular injections. In addition, the plunger tack isalso useful with hypodermic devices or ampoules that provide a chamber ,containing-botha medicament and a hypodermic needle through which the injection is made. Such ampoules may include multiple chambersfor premixing a medicament with at least one other medicament and injecting the mixture, either subcutaneously or intramuscularly. All such ampoules are generically referred to hereinafter as contained-needle" type hypodermic devices or ampoules and they are described in greater detail in the copending U. S. Pat. application of I-Iurschman et al., Ser. No. 114,493, filed Feb. 11, 1971.

ln the contained-needle type ampoule, the needle'is carried by the plunger which also serves to close the rearward end of the chamber. The pointed end of the needle is disposed adjaeent 'a puncturable wall pro-- vided in an inert rubber diaphragm which closes the forward endof the chamber. Accordingly, the plunger is formed of aresilient materialand it is disposed in a compressed configuration within the chamber to provide sealing engagement with the internal, sidewall surface of the chamber.

The contained-needle type of ampoule is frequently used incombination with an applicator for actuating the ampoule to project the pointed end of the needle through the puncturable wall of the ampoule and then into the patient while reducing the volume of the medicament-containing chamber to express the medicament through the needle and into the patient. The applicator includes a spring biased, movable piston, coaxially disposed with the chamber, and arranged to provide the injection function upon forward movement into engagement with the plunger and advancement of the plunger in sliding, sealing engagement with the sidewall of the chamber.

In order to safely contain the medicament and prevent chemical reactions therewith, the sidewall of the cylindrical chamber is generally formed of inert glass tubing. The transparency of the glass sidewall permits visual inspection of the medicament.

The material which forms the plunger must also be inert so as to avoid chemical reactions with the medicament resulting in the contamination thereof. Natural and synthetic rubber materials have been found satisfactory for these purposes and the specific material selected is related to the particular medicament with which it is to be used. For example, natural rubber has been found satisfactory for use with insulin and narcotics, butyl rubber is employed with birth control medica- 2 a ments and some vaccines, and chloro-butyl rubber is used with atropine sulphate.

Although the use of such rubber materials has been found satisfactory with regard to the prevention of chemical reactions and medicament contamination, theiruse has resulted in additional problems which have not been satisfactorily resolved by the prior art.

Initially, it is noted that such rubber materials provide a high coefficient of friction with the glass sidewall of the chamber. In some instances, the static friction developed between the plunger and the glass sidewall of the chamber has been of a sufficient degree to result in the breakage of the glass upon forward movement of the piston into driving engagement with the frictionally immobilized plunger. Specifically, the forces transmittted by the piston to the rearward portions of the plunger result in sufficient lateraldeformation of radial expansion of the frictionally bound plunger to. break the glass sidewall of the chamber.

Further, such rubber materials tend to oxidize with the passage of time and such oxidation is accelerated upon exposure to heat and light. As a result of such oxidation, the rubber material forming the plunger becomes less resilient or stiffer and the problems relating to the breaking of the glass sidewall of the chamber become more pronounced.

In order to reducethe coefficient of friction and/or the frictional forces developed between the plunger and the sidewall of the chamber, the prior art teaches the use of silicone lubricants applied to the outer surfaces of the plunger. Although the use of silicone has alleviated the problem to a degree, the silicone tends to be absorbed by the rubber material of the plunger and its effectiveness as a lubricant is correspondingly decreased. In addition, the use of a silicone lubricant has I created further problems which are unrelated to the reduction of frictional forces. v i

i The initial assembly of the plunger within the chamber may necessarily involve the introduction of the plunger into the chamber adjacent the forward end thereof and the sliding, rearward movement of the plunger to its assembled position adjacent a rearward portion of the chamber. The reasons for this reverse assembly procedure will become more apparent below, however, it is presently noted that this reverse assembly procedure results in the transfer of some of the silicone lubricant from the plunger to the internal surface of the chamber and a silicone wipe coat is essentially applied to the sidewall of the chamber.

The medicament which is subsequently disposed within the chamber is, of course, contacted with the silicone wipe coat and contaminated with the silicone. Consequently, the silicone must be of acceptable medical purity to prevent such contamination from being harmful to the patient.

Although the silicone contamination is not harmful per se, the medication vial acquires a cloudy appearance as a result of it being coated by the silicone. The cloudy appearance is undesirable for obvious reasons and itdoes render the visual inspection of the medicament difficult, if not impossible, in. some cases.

The prior art also teaches the use of various plunger arrangements designed to alleviate the frictional problems discussed above. Such plunger arrangements frequently rely upon the presence of a piston structure to provide an adequate seal between the plunger and sidewall of the chamber.

One such arrangement is shown in U. S. Pat. No. 2,660,168 wherein a rubber-like plunger having a rounded forward end portion and a rearwardly disposed recess arranged to receive an extension of a piston is provided. The rearward end portion of the plunger is laterally expanded by a laterally enlarged portion of the piston extension to provide static as well as dynamic sealing engagement between the plunger and the sidewall of the chamber. The forward end of the plunger is elongated upon advancement of the piston so as to reduce the plungers lateral dimensions and facilitate the movement of the plunger.

Thisstructure is unsatisfactory in some applications due to the necessity of maintaining the plunger in engagement with the piston in order to assure static sealing and the proper retention of the plunger within the chamber. Specifically, it is frequently desirable to assemble and fill the contained-needle type ampoule without installing it in an applicator which provides the piston.

Further, the plunger structure forms a single seal which is provided by the enlarged portion of the piston with the chamber sidewall. It is necessary to substantially elongate the forward portion of the plunger, resulting in a substantially rounded shape, to provide any significant reduction in' the frictional forces, since the single seal must be maintained in tight engagement with the sidewall. The highly rounded forward portion of the plunger fails to completely empty the chamber upon injection due to the rounded, elongated configuration thereof. In addition, once the plunger has been elongated during the course of an injection, any momentary hesitation in the advancement of the piston will result in aspiration due to the return of the forward end of the plunger to an unelongated configuration.

Another prior art engagement is shown in U. S. Pat.

No. 2,895,773. That patent teaches the mounting of a rubber-like cap, which includes laterally projecting rings or lips'and functions as a plunger, over a piston head. The cap includes a recess for receiving the piston head and the head is provided with dimensions larger than those of the'recess in order to laterally and axially expand or stretch the cap and retain it in the mounted position in sealing engagement with the sidewall of the chamber. Upon advancement of the plunger, the rings or lips roll in a radially inward direction about adjacent ends or shoulders of the piston to facilitate movement of the plunger.

The usefulness of this arrangement is also limited as it does not lend itself to the contained-needle type hypodermic device wherein the ampoule is assembled, filled with a medicament and shipped without an applicator which provides the piston.

The oxidation of the rubber plunger material in this structure is especially critical since the loss in resiliency resulting therefrom inhibits both the deformation of the plunger and the rolling action of the rings. Further the cap and piston head must be carefully sized and assembled to assure that the frictional forces resisting movement result in theradially inward displacement of the forward ring. Specifically, the forward ring must engage the chamber wall at an appropriate contact angle in order to assure that the components of the reactionary forces developed result in radially inward displacement of the ring.

The prior art also teaches the use of a variety of plunger tacks which are designed primarily to facilitate engagement of the plunger by the piston and/or for purposes of aspirating the hypodermic device. Accordingly, such a plunger tack is generally arranged to pro vide a fixed connection between the piston and the plunger. To that end, the tack may be threadedly engaged with the piston and integrally, permanently connected to the plunger by the chemical and/or mechanical bonding thereto of a portion of the tack disposed within the plunger.

Such prior art tacks are not intended to resolve the frictional problems discussed above. Contrarily, they may tend to promote such problems in some instances as a result of their configuration and fixed connections to the plunger. Specifically, the configuration ofv the portion of the tack within the plunger and the fixed connection therewith results in force transmission characterized by undesirably large, laterally directed components. For example, such tendencies exist when the portion of the tack disposed within the plunger is provided with enlarged lateral dimensions or a conical shape having increasing rearward dimensions.

As will become more apparent hereinafter, the prior art teachings regarding the integral connection between the tack and the plunger result in a significantly more costly structure involving relatively costly production techniques in comparison with the teachings of the present invention. For example, the provision of threaded engagement means for the tack results in obvious additional costs. When the tack is connected to the plunger by molding it in place as the plungeris being formed, the plunger molding process is complicated and rendered more costly by the partial disposition of the tack within the plunger molding chamber since such necessitates additional manipulatingsteps as well as the use of specially arranged molds.

SUMMARY OF INVENTION The present invention provides a plunger tack for use with a deformable plunger adapted 'to be sealingly, frictionally disposed in a compressed configuration within an axially extending, laterally constrictive, medicament containing chamber of a hypodermic device. The plunger tack is adapted to be engaged by a spring biased movable piston and to transmit force to a forward portion of the plunger which is disposed adjacent the direction of movement. The forces are transmitted by the tack so as to provide the plunger with an elongated deformed configuration having reduced lateral dimensions and to thereby reduce the static and dynamic frictional forces between the plunger and the chamber while retaining sealing engagement between the plunger and the chamber.

In the illustrated embodiment, the tack has a rigid configuration comprising a flange and a shank. The shank is arranged to be received within a recess in the plunger with lateral clearance and, thereafter, to be retained in engagement with the plunger solely by frictional forces resulting from the compression of the plunger by the laterally constrictive chamber. The flange has lateral dimensions larger than those of the recess and it is exposed adjacent a rearward portion of the plunger to provide a planar piston engaging face adapted to be struck by the piston without mechanically or otherwise interlocking therewith.

The reduction of the static and dynamic frictional forces developed between the plunger and the chamber is of a sufficient magnitude to substantially eliminate I fective fluid seal with the sidewall of the medicament containing chamber. It should be appreciated that the reduction in frictional forces is achieved while retaining both the forward and rearward portions of the plunger in sliding, sealing engagement with the sidewall of the chamber.

The tack also permits the plunger to be initially assembled within the chamber by insertion from either end thereof so as to eliminate the reverse assembly problems of the prior art. Specifically, the initial positioning of the tack within the recess of the plunger provides a degree of rigidity thereto as well as the dimension reducing function upon advancement of the disposed within an axially extending recess 12 in an plunger into the chamber during the assembly thereof.

Accordingly, the production inconveniences of advancing the plunger through the length of the chamber are eliminated. i

As indicated above, the tack is retained within the recess of. the plunger solely by frictional engagement when the plunger is in a compressed configuration within the chamber. This means of tack engagement has been found to adequately retain the tack and the plunger in position throughout the subsequent assembling process and injection use of the hypodermic device. Thus, the plunger tack of the present invention is well suited for use in the contained-needle type hypodermic device wherein the plunger may be preferably employed to close the rearward end of the medicament containing chamber without the assistance of a plunger expanding piston or additional closure means as required by prior art structures. I

It should be appreciated that the tack and plunger of the present invention may be separately manufactured and subsequently assembled at a lower cost than that of the integrally molded tackand plunger combination of the prior art. The cost reduction is achieved in part through the simplification of the plunger molding process since a relatively less intricate mold may be employed and it is not necessary to carry out the manipulative processes of partially disposing the tack within the mold during molding of the plunger.

. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a plunger tack disposed within a recess of a plunger in an uncompressed condition according to the present invention;

FIG. 2 is a cross-sectional view showing the plunger tack and plunger of FIG. I inserted within an ampoule with the plunger tack being contacted by a movable piston and the plunger being in a compressed condition; and

FIG. 3 is a fragmentary, cross-sectional view similar to FIG. 2 showing the plunger in an elongated deformed condition upon advancement of the movable piston.

DETAILED DESCRIPTION OF THE DRAWINGS Referring to FIG. 1, there is shown a plunger tack 10 elastically deformable plunger 14. The tack 10 includes a circular head or flange member 16 and an axially projecting, cylindrical shank member 18. The tack is formed of a rigid plastic material having a relatively high impact strength such as nylon.

The plunger includes cylindrical rearward and forward portions 20 and 22, respectively, which are connected by an intermediate portion 24 having a decreased diameter. The forward and rearward portions are dimensioned to provide a sliding,'sealing interference fit within the medicament containing chamber of,

a hypodermic device.

The recess 12 is also cylindrical and includes an axially extending sidewall 12a,a bottom fa'ce 12b, and a recess opening 12c in a rearward face 20a of the plunger. I

The forward portion 22 of the plunger includes a tapered recess 26 which defines an annular lip 28. The

recess 26 and the lip 28 are provided for receiving and retaining the base portion of a hypodermic needle, as described more fully below.

As shown in FIG. 1, the flange member 16 has a diameter larger than that of the recess 12 and, accordingly, it laterally extends over a portion of the rearward face 20a of the plunger. The shank member 18 of the tack is provided with a diameter smaller than that of the recess 12 and it is received with clearance within the recess when the plunger is inan uncompressed condition. Accordingly, the tack maybe easily and quickly inserted within the recess, of the uncompressed plunger during assembly. y The axial length of the shank member 18 is greater than the axial depth of the recess 12 whenthe plunger is in an uncompressed condition. Thus, when the tack is inserted within the recess, the flange member is axially spaced from the rearward face 20a of the plunger when the shank driving face of the tack is disposed against the bottom facel2b of the recess. I

Referring to FIG. 2, the tack 10 and plunger 14 are shown disposed within a single chamber ampoule 30 of the contained-needle type and a portion of a piston 32 is shown in contact with the tack 10. The piston 32 is a component of an applicator (not shown) which retains the ampoule in a stationary position permitting relative axialforward movement of the piston to advance the plunger and perform the injection function.

The ampoule 30 is adapted to perform a subcutaneous injection and includes a cylinder 34. The cylinder 34 is preferably made from inert glass tubing and it has a radially extending annular bead 36 adjacent the forward end thereof. The forward end of the cylinder is closed by a diaphragm 38which is pressed against it by a plastic clip 40. The clip 40 is cup-shaped and has an inner annular groove 42 in its cylindrical sidewall which snaps over the bead36. The: clip includes a bottom wall 40a having a central aperture 40b therethrough. p

The diaphragm 38 is formed of a suitably inert rubber material and it is shaped to function in accordance with the teachings of U. S. Pat. No. 3,094,988 to Dunmire. The diaphragm includes a centrally located, needle guiding and liquid sealing gland 44. The gland extends through the aperture 40b in the bottom wall of the clip and an axial needle passage 46 extends into the upper end of the gland from the inside thereof. The needle 7 passage terminates short of the opposite side of the gland to form a thin, easily puncturab le wall 48 which closes the bottom of the passage.

The rearward end of the cylinder is closed by the plunger 14 which is initially disposed adjacent the rearward end of the cylinder. The internal diameter of the cylinder is smaller than the external diameter of the rearward and forward portions of the plunger when the plunger is in a relaxed or uncompressed condition. The diameters are selected to compress the plunger portions a predetermined amount upon the assembly thereof within the cylinder. Consequently, the plunger is disposed within the cylinder in a compressed configuration or condition to thereby provide sealing engagement or an interference fit between the rearward and forward portions of the plunger and the sidewall of the cylinder. The intermediate portion 24 of the plunger is dimensioned to fit with clearance within the cylinder.

In contrast, the tack permits direct insertion of the plunger into the rearward end of the cylinder as it acts somewhat like an inserting mandrel or tool by virtue of its more rigid structure. As will become more apparent hereinafter, the tack also tends to reduce the lateral dimensions of the plunger as it is being inserted within the cylinder.

When the ampoule is assembled, the plunger, the cylinder, and the diaphragm cooperate to define a chamber 50 which is substantially filled with a liquid medicament to'be injected.

A hypodermic needle 52 is disposed within the recess 26 of the plunger and the needle is in substantial axial alignment with the cylinder 34. The needle includes a circular base 54 which is mounted in the recess 26 by snapping the peripheral edge of the base under the annular lip 28 of the plunger. The needle includes an axially projecting cannula 56 having the pointed end thereof received within the needle passage 46. Flow into the cannula from the chamber 50 occurs through an opening 58 in the cannula wall adjacent the base of the needle.

.The axial distance between the bottom face 12b of the recess 12 and the bottom face 26a of the recess 26 is of a sufficient thickness to provide a moisture vapor barrier for the medicament. In typical applications, a suitable barrier is obtained when the axial distance between the bottom faces ranges from about 0.075 inches to about 0.100 inches.

As indicated above, the shank 18 of the tack fits within the recess 12 with radial clearance when the plunger is in an uncompressed condition. Upon assembly of the plunger within the cylinder, the lateral compression of the plunger is accommodated in part by the constriction of the recess so as to contiguously dispose the sidewall 12a thereof against the shank 18 of the tack and frictionally retain the tack in position. The tack and, more particularly, the shank is retained within the recess solely by the frictional forces developed upon constriction of the recess and an interference fit is provided therebetween.

When the plunger is disposed within the cylinder, the axial depth of the recess 12 is somewhat increased but it typically remains slightly less than the axiallength of the shank member. The side of the flange 16 adjacent to the plunger defines an annular flange driving face 16a which may be axially spaced a small distance from the rearward face 20a of the plunger. However, it should be understood that this spacing between the flange driving face and the rearward face of the plunger, although preferable, is not critical to the teachings of the present invention and the flange driving face may be disposed against the. rearward faceof the plunger when the latter is assembled within the cylinder.

The constriction and the slight axial elongation of the recess 12 are representative of dimension changes in the plunger as a whole resulting from the laterally compressive forces exerted on the plunger by the cylinder. The constriction and the elongation are indicative of a reduction in the lateral dimensions of the plunger. It is believed that thisreduction of lateral dimensions has a tendency to be uniform throughout the axial length of the plunger including the forward and rearward portions thereof. This is believed to be a result of the shank and the recess having uniform dimensions throughout their axial length and, therefore, initially providing a uniform clearance fit for accommodating radially inward displacement of theplunger.

The side of the flange member 16 which is spaced from the plunger defines a planar piston engaging face 16b. Although FIG. 2 shows the piston 32 in driving engagement with the face 16b, the piston 32 is normally initiallyspaced about one fourth inch from the face 16b and the piston is releasably locked in that position by a triggering mechanism. A biasing force is exerted on the piston by a spring which is preloaded to 6 0 pounds. The piston engaging face is arranged to be struck by the piston 32 upon release of the triggering mechanism to cause forward axial movement thereof and to transmit driving force to the plunger. The piston engaging face does not mechanically interlock orotherwise connect with the piston. Consequently, abutting engagement is provided between the tack and the piston upon forward movement of the latter and relative axial movement results upon rearward, withdrawal of the piston.

As shown in FIG. 3, the plunger 14 is provided with an elongated deformed configuration, as distinguished from the slight axial elongation thereof when it is merely disposed in the cylinder, upon advancement of the piston 32 and the movement of the flange driving face 16a into driving engagement with the rearward face 20a of the plunger. The shank member 18 and the shank driving face 18a transmit the major driving force of the piston to regions of the plunger adjacent the forward portion 22 thereof providing the plunger with the elongated deformed configuration and thereby further reducing the lateral dimensions thereof.

Consequently, the frictional force developed intermediate the plunger and the cylinder 34 is correspondingly reduced and, more particularly. the static frictional force developed just prior to the commencement of plunger movement is sufficiently reduced to prevent the binding of the plunger within the cylinder. Thus, the lateral dimensions of the plunger are not increased upon forward movement of the plunger and the prior art problems relating to the breakage or shattering of the cylinder are substantially eliminated.

The desired transmission of the piston driving forces to the forward portion of the plunger'is achieved in part by the disposition of the bottom face 12b of the recess,

which is engaged by the shank driving face 18a, at an axially forward location with respect to the rearward portion 20 of the plunger. It is presently believed that The reduction in lateral dimensions of the plunger and the static frictional force developed is achieved without'loss of the effectiveness of the seals provided by the rearward and forward portions of the plunger with the sidewall of the cylinder. Furthermore, the forward portion of the plunger is not excessively, laterally deformed and it retains a configuration which assures the appropriate mounting of the hypodermic needle and the injection of substantially all of the medicament contained within the chamber.

The invention is not restricted to the slavish imitation of each and every one of the details described above, which have been set forth merely by way of example with the intent of most clearly setting forth the teaching of the invention. Obviously, devices may be provided whichchange, eliminate, or add certain specific details without departing from the invention.

'What isclaimed is: i

l. The combination'of a deformable plunger, force transmittingmeans, and plunger compressing means comprising an axially extending, laterally constrictive, medicament containing chamber of a hypodermic device housing said plunger, said plunger having forward and rearward portions and being sized to be received in said chamber in a compressed configuration and frictionally, sealingly engaged therein, said force transmitting means comprising a plunger tack adapted to be engaged bya movable piston and transmit force to said plunger to provide forward movement thereof within said chamber, said tack including head means which is exposed at the rearward portion of the plunger and which is adapted to be engaged by a piston and including plunger engaging means comprising a cylindrical shank member having a uniform diameter along its entire axial length and extending axially from said head means into a recess in said plunger, said recess having a uniform diameter along its entire axial length and having a depth less than the axial extent of said shank said plunger engaging means being substantially discrete of said plunger and dimensioned to fit within said recess with lateral clearance when said plunger is in an uncompressed configuration, said plunger engaging means being retained and supported within said recess solely by frictional engagement with said plunger when the plunger is in said compressed configuration and being arranged to transmit force to said forward portion of said plunger to provide said plunger with an elongated deformed configuration and reduce the lateral dimensions and static frictional force between the plunger and said chamber while retaining sealing en- 10 gagement between the chamber and both the front and rearward portions of the plunger.

2. The combination as set forth in claim 1 wherein j said head means comprises a laterally extending flange member having lateral dimensions larger than those of said recess and defining a piston engaging face and an oppositely disposed flange driving face.

3. The combination as set forth in claim 2 wherein said flange driving face engages a rearward extremity of said plunger when said plunger is provided with said elongated, deformed configuration during forward movement thereof.

4. The combination as set forth in claim 2 wherein said forward and rearward portions of said plunger are connected by a central portion having smaller-lateral dimensions, said central portion fitting with lateral clearance in said chamber when said plunger is in said compressedconfiguration.

5. The combination of a deformable plunger having rearward and forward portions, force transmitting means, and an axially extending, laterally constrictive, medicament containing chamber of a hypodermic device, said plunger being disposed in a compressed configuration and frictionally, sealingly engaged within said chamber, said force transmitting means comprising a plunger tack adapted to be engaged by a movable piston and transmit force to .said plunger to provide forward axial movement thereof within said chamber, said plunger tack comprising head means which is exposed at the rearward portion of the plunger and. which is adapted to be engaged by said piston and including plunger engaging means having a single, uniform lateral dimension and extending axially from said head means into a recess in said plunger with lateral clearance when said plunger is in an uncompressed configuration, said recess having a single, uniform lateral dimension and having a depth less than the axial extent of said plunger engaging means said chamber having internal lateral dimensions smaller than the lateral dimensions of said plunger when in an uncompressed configuration to thereby elastically compress said plunger a predetermined amount into said compressed configuration so as to compressively, frictionally retain said plunger engaging means within said recess and uniformly engage said plunger engaging means along the axial length thereof within said recess.

6. The combination as set forth in claim 5 wherein said plunger engaging means has lateral dimensions it smaller than those of said recess when said plunger is in an uncompressed configuration and said predeter: mined compression of said plunger provides said recess with reduced lateral dimensions so as to compressively, frictionally retain said plunger engaging means therein.

7. The combination of a deformable plunger, force transmitting means, an axially extending, laterally constrictive, medicament containing chamber of a hypodermic device housing said plunger, and a movable piston mounted in said hypodermic device for reciprocal 1 1 prising a plunger tack arranged to be engaged by said movable piston and to transmit force to said plunger to provide forward, axial movement thereof within said chamber, said plunger tack comprising head means which is exposed at the rearward portion of the plunger and plunger engaging means extending axially from said head means into said recess and having a single, uniform lateral dimension, said plunger engaging means being retained within said recess solely by frictional engagement with said plunger when the plunger is in said compressed configuration, said recess having a single, uniform lateral dimension and having a depth less than the axial extent of said plunger engaging means said head means including a piston engaging being arranged to engage a rearward extremity of said plunger. 

1. The combination of a deformable plunger, force transmitting means, and plunger compressing means comprising an axially extending, laterally constrictive, medicament containing chamber of a hypodermic device housing said plunger, said plunger having forward and rearward portions and being sized to be received in said chamber in a compressed configuration and frictionally, sealingly engaged therein, said force transmitting means comprising a plunger tack adapted to be engaged by a movable piston and transmit force to said plunger to provide forward movement thereof within said chamber, said tack including head means which is exposed at the rearward portion of the plunger and which is adapted to be engaged by a piston and including plunger engaging means comprising a cylindrical shank member having a uniform diameter along its entire axial length and extending axially from said head means into a recess in said plunger, said recess having a uniform diameter along its entire axial length and having a depth less than the axial extent of said shank said plunger engaging means being substantially discrete of said plunger and dimensioned to fit within said recess with lateral clearance when said plunger is in an uncompressed configuration, said plunger engaging means being retained and supported within said recess solely by frictional engagement with said plunger when the plunger is in said compressed configuration and being arranged to transmit force to said forward portion of said plunger to provide saiD plunger with an elongated deformed configuration and reduce the lateral dimensions and static frictional force between the plunger and said chamber while retaining sealing engagement between the chamber and both the front and rearward portions of the plunger.
 2. The combination as set forth in claim 1 wherein said head means comprises a laterally extending flange member having lateral dimensions larger than those of said recess and defining a piston engaging face and an oppositely disposed flange driving face.
 3. The combination as set forth in claim 2 wherein said flange driving face engages a rearward extremity of said plunger when said plunger is provided with said elongated, deformed configuration during forward movement thereof.
 4. The combination as set forth in claim 2 wherein said forward and rearward portions of said plunger are connected by a central portion having smaller lateral dimensions, said central portion fitting with lateral clearance in said chamber when said plunger is in said compressed configuration.
 5. The combination of a deformable plunger having rearward and forward portions, force transmitting means, and an axially extending, laterally constrictive, medicament containing chamber of a hypodermic device, said plunger being disposed in a compressed configuration and frictionally, sealingly engaged within said chamber, said force transmitting means comprising a plunger tack adapted to be engaged by a movable piston and transmit force to said plunger to provide forward axial movement thereof within said chamber, said plunger tack comprising head means which is exposed at the rearward portion of the plunger and which is adapted to be engaged by said piston and including plunger engaging means having a single, uniform lateral dimension and extending axially from said head means into a recess in said plunger with lateral clearance when said plunger is in an uncompressed configuration, said recess having a single, uniform lateral dimension and having a depth less than the axial extent of said plunger engaging means said chamber having internal lateral dimensions smaller than the lateral dimensions of said plunger when in an uncompressed configuration to thereby elastically compress said plunger a predetermined amount into said compressed configuration so as to compressively, frictionally retain said plunger engaging means within said recess and uniformly engage said plunger engaging means along the axial length thereof within said recess.
 6. The combination as set forth in claim 5 wherein said plunger engaging means has lateral dimensions smaller than those of said recess when said plunger is in an uncompressed configuration and said predetermined compression of said plunger provides said recess with reduced lateral dimensions so as to compressively, frictionally retain said plunger engaging means therein.
 7. The combination of a deformable plunger, force transmitting means, an axially extending, laterally constrictive, medicament containing chamber of a hypodermic device housing said plunger, and a movable piston mounted in said hypodermic device for reciprocal movement along an axis corresponding with that of said chamber, said plunger having an axial recess and having lateral dimensions larger than the internal dimensions of said chamber and arranged to be disposed within said chamber in a compressed configuration to provide a sliding, sealing interference fit therein, said movable piston being axially aligned with said force transmitting means, said force transmitting means comprising a plunger tack arranged to be engaged by said movable piston and to transmit force to said plunger to provide forward, axial movement thereof within said chamber, said plunger tack comprising head means which is exposed at the rearward portion of the plunger and plunger engaging means extending axially from said head means into said recess and having a single, uniform lateral dimension, said plunger engaging means being retained within saId recess solely by frictional engagement with said plunger when the plunger is in said compressed configuration, said recess having a single, uniform lateral dimension and having a depth less than the axial extent of said plunger engaging means said head means including a piston engaging face disposed adjacent said piston and arranged to provide butting contact therewith during forward movement of said plunger and to permit relative axial movement therebetween upon rearward movement of said piston.
 8. The combination as set forth in claim 7 wherein said piston engaging face has a planar configuration.
 9. The combination as set forth in claim 8 wherein said head means includes an annular driving face oppositely disposed from said piston engaging face, said annular driving face having a planar configuration and being arranged to engage a rearward extremity of said plunger. 